This invention relates to flat-panel displays and, in particular, to the configuration of a spacer system utilized in a flat-panel display, especially one of the field emission type.
A flat-panel field emission display is a thin, flat display which presents an image on the display""s viewing surface in response to electrons striking light-emissive material. The electrons can be generated by mechanisms such as field emission and thermionic emission. A flat-panel field emission display typically contains a faceplate (or frontplate) structure and a backplate (or baseplate) structure connected together through an annular outer wall. The resulting enclosure is held at a high vacuum. To prevent external forces such as air pressure from collapsing the display, one or more spacers are typically located between the plate structures inside the outer wall.
FIGS. 1 and 2, taken perpendicular to each other, schematically illustrate part of a conventional flat-panel field emission display such as that disclosed in Schmid et al, U.S. Pat. No. 5,675,212. The components of this conventional display include backplate structure 20, faceplate structure 22, and a group of spacers 24 situated between plate structures 20 and 22 for resisting external forces exerted on the display. Backplate structure 20 contains regions 26 that selectively emit electrons. Faceplate structure 22 contains elements 28 that emit light upon being struck by electrons emitted from electron-emissive regions 26. Each light-emissive element 28 is situated opposite a corresponding one of electron-emissive regions 26.
Each of spacers 24, one of which is fully labeled in FIGS. 1 and 2, consists of main spacer wall 30, end electrodes 32 and 34, a pair of face electrodes 36, and another pair of face electrodes 38. End electrodes 32 and 34 are situated on opposite ends of spacer wall 30 so as to contact plate structures 20 and 22. Face electrodes 36 form a continuous U-shaped electrode with end electrode 32. Face electrodes 38 form a continuous U-shaped electrode with end electrode 34.
It is desirable that spacers in a flat-panel field emission display not produce electrical effects which cause electrons to strike the display""s faceplate structure at locations significantly different from where the electrons would strike the faceplate structure in the absence of the spacers. The net amount that the spacers cause electrons to be deflected sideways should be close to zero. Achieving this goal is especially challenging when, as occurs In the conventional display of FIGS. 1 and 2, the spacing between consecutive wall-shaped spacers is more than two electron-emissive regions. If spacers 24 cause net electron deflections, the net deflections of electrons emitted from regions 26 located different distances away from the nearest spacer 24 are typically different. This can lead to image degradation such as undesired features appearing on the display""s viewing surface.
Face electrodes 36 and 38 are utilized to control the electric potential field along spacers 24 in order to reduce their net effect on the trajectories of electrons moving from regions 26 to elements 28. However, as discussed in Schmid et al, spacers 24 are typically made by a process in which large sheets of wall material having double-width strips of electrodes 36 and 38 formed on the sheets are mechanically cut along the centerlines of electrodes 36 and 38. Due to mechanical limitations in performing the cutting operation, the width of each face electrode 36 or 38 can vary along its length.
In turn, the variation in face-electrode width causes the electrical effect that spacers 24 have on the electron trajectories to vary along the spacer length. The net electron deflection resulting from spacers 24 thus varies along their length. Even if the net electron deflection is largely zero at one location along the spacer""s length, the net electron deflection at other locations along the spacer""s length can cause substantial image degradation. It is desirable to avoid image degradation that arises from width variations of face electrodes that contact end electrodes. However, attempts at correction of the distortion due to interference with intended electron trajectories meet with effects caused by construction imperfections.
Imperfections in the construction of the wall results include variations in wall resistance uniformity and dicing alignment tolerance. This causes a zero current shift variation, e.g., a variation in the electron beam along the wall due to improper electrical potential on the wall surface. Zero current shift variation causes image degradation due to visible distortion of a display generated by the beam.
The conventional approach to attempting to prevent zero current shift has been to apply wall coatings and install and connect separate electrodes. However, these conventional approaches are complex and expensive. Further, they have the effect of rendering testing for defects nearly impossible. Quality testing is an often crucial requirement in fabrication of flat panel displays. Interfering with defects testing is problematic.
What is needed is a method for minimizing zero current shift variation in a flat panel field emission display. What is also needed is a method of fabricating a flat panel field emission display which minimizes zero current shift distortion in electron beams and resultant image degradation. Further, what is needed is a method of fabricating flat panel field emission display which minimizes zero current shift distortion in electron beams and resultant image degradation, and which facilitates testing and failure analysis. Further still, what is needed is a method which achieves these advantages without undue complexity and expense.
In accordance with one embodiment of the invention, a segmented face electrode overlies a face of a main portion of a spacer situated between a pair of plate structures of a flat-panel display. The segmented face electrode is spaced apart from both plate structures, one of which provides the display""s image, and also from any spacer end electrodes contacting the plate structures. The face electrode is segmented laterally. That is, the face electrode is divided into a plurality of electrode segments spaced apart from one another as viewed generally perpendicular to either plate structure.
The flat-panel display is normally a flat-panel field emission display in which the image-producing plate structure emits light in response to electrons emitted from the other plate structure. As electrons travel from the electron-emitting plate structure to the light-emitting plate structure, the laterally separated segments of the face electrode typically cause the electrons to be deflected in such a manner as to compensate for other electron deflection caused by the spacer. By suitably choosing the location and size of the electrode segments, the net electron deflection caused by the spacer can be quite small.
The segments of the face electrode normally reach electric potentials largely determined by resistive characteristics of the spacer. Although the potential along the spacer generally increases in going from the electron-emitting plate structure to the light-emitting plate structure, the potential is largely constant along each electrode segment. The effect of this constant potential produces the compensatory electron deflection.
Division of the face electrode into multiple laterally separated segments facilitates achieving appropriate compensatory electron deflection along the entire active-region length of the spacer, the spacer""s length being measured laterally, generally parallel to the plate structures. In particular, the value of electric potential that each electrode segment needs to attain in order to cause the requisite amount of compensatory electron deflection varies with distance from the plate structures in approximately the same way that the resistive characteristics of the spacer cause the segment potential to vary with distance from the plate structures. Once the desired segment potential is established for one distance from the plate structures, the distance from each segment to the plate structures can vary somewhat without significantly affecting the amount of compensatory electron deflection.
In contrast, consider what would happen if (a) a non-segmented face electrode were substituted for the present segmented face electrode and (b) the non-segmented face electrode were placed in approximately the same position over the main spacer portion as the segmented face electrode. The entire non-segmented face electrode would be at substantially a single electric potential. If the non-segmented face electrode were tilted relative to the plate structure for some reason, e.g., due to fabrication misalignment, one vertical slice through the non-segmented face electrode might be at largely the correct potential. However, a vertical slice anywhere else through the non-segmented face electrode would normally be at a wrong potential, leading to a wrong amount of compensatory electron deflection. Segmentation of the face electrode in the present flat-panel display provides tolerance in positioning the electrode segments to achieve the desired compensatory electron deflection across substantially all the active-region length of the spacer, thereby overcoming the lack of positioning tolerance that would occur with a non-segmented face electrode.
The amount of compensatory electron deflection caused by each segment of the present face electrode depends on the segment""s width. Accordingly, the widths of the electrode segments normally need to be controlled well.
In applying the invention""s teachings to the fabrication of a flat-panel display, particularly one of the field emission type, a masking step is typically utilized in defining the widths of the segments of the face electrode. In general, better dimensional control can be achieved with a masking operation, especially photolithographic masking as is normally utilized to implement the masking step, than with a mechanical cutting operation as employed conventionally by Schmid et al to define the widths of the face electrodes in U.S. Pat. No. 5,675,212. The net electron deflection arising from the presence of a spacer can thus more uniformly be made closer to zero in the invention than in Schmid et al.
One embodiment of the present invention provides a method for minimizing zero current shift and its variation in a flat panel field emission display. The present invention also provides a method of fabricating a flat panel field emission display which minimizes zero current shift distortion in electron beams and resultant image degradation. Further, the present invention provides a method of fabricating flat panel field emission display which minimizes zero current shift distortion in electron beams and resultant image degradation, and which facilitates testing and quality control. Further still, the present invention provides a method which achieves these advantages, which is simple and inexpensive.
In one embodiment, the length of the segment electrodes is defined to be effective to minimize zero current shift variation. A component of zero current shift variation resulting from wall resistance variations is determined. Another component of zero current shift variation resulting from fabrication misalignment is also determined. Both components of zero current shift variation are combined in a specific manner, which is operated upon to define a length at which zero current shift variation is minimal.
In one embodiment, flat panel field emission displays are fabricated utilizing segment electrodes of the lengths determined to minimize zero current shift variation. In one embodiment, the segment electrodes are sufficiently long to allow individual electrical testing thereof. Importantly, fabrication of flat panel field emission displays with segment electrodes of the defined length for minimizing zero current shift adds neither undue complexity nor expense.
In one embodiment, individual electrical testing of segment electrodes is applied to promote quality assurance during fabrication. Conventionally, individual electrical testing of segment electrodes was precluded due to their small size and unmanageably large number. Importantly, in one embodiment, individual electrical testing of segment electrodes is applied to enable quality control.